Fix verbatim control flow size effects.

docs/yul.rst

@@ -1094,7 +1094,8 @@ the compiler. Violations of these restrictions can result in
 undefined behavior.
 
 - Control-flow should not jump into or out of verbatim blocks,
-  but it can jump within the same verbatim block.
+  but it can jump within the same verbatim block. In particular,
+  reverting or returning from the block is *not* allowed.
 - Stack contents apart from the input and output parameters
   should not be accessed.
 - The stack height difference should be exactly ``m - n``

libyul/ControlFlowSideEffects.h

@@ -68,6 +68,12 @@ struct ControlFlowSideEffects
 
 		return controlFlowSideEffects;
 	}
+
+	/// @returns the worst-case control flow side effects.
+	static ControlFlowSideEffects worst()
+	{
+		return ControlFlowSideEffects{true, true, true};
+	}
 };
 
 }

libyul/backends/evm/EVMDialect.cpp

@@ -566,7 +566,7 @@ BuiltinFunctionForEVM EVMDialect::createVerbatimFunction(size_t _arguments, size
 		1 + _arguments,
 		_returnVariables,
 		SideEffects::worst(),
-		ControlFlowSideEffects{},
+		ControlFlowSideEffects::worst(), // Worst control flow side effects because verbatim can do anything.
 		std::vector<std::optional<LiteralKind>>{LiteralKind::String} + std::vector<std::optional<LiteralKind>>(_arguments),
 		[=](
 			FunctionCall const& _call,

test/libyul/yulOptimizerTests/unusedStoreEliminator/store_before_terminating_verbatim_revert.yul

@@ -0,0 +1,20 @@
+{
+    let x := 0
+    let y := 1
+    sstore(x, y)
+    // opcodes: PUSH1 0x00 DUP1 RETURN
+    // SSTORE is not redundant due to the RETURN hidden in the verbatim block. It must not be removed.
+    verbatim_0i_0o(hex"600080F3")
+    revert(0,0)
+}
+// ----
+// step: unusedStoreEliminator
+//
+// {
+//     {
+//         let x := 0
+//         sstore(x, 1)
+//         verbatim_0i_0o("`\x00\x80\xf3")
+//         revert(0, 0)
+//     }
+// }